The main objective of the proposed research is to purify the ribonucleotide reductase from Ehrlich tumor cells so that the properties of this enzyme can be unequivocally established. It is felt that by defining the properties and requirements of this enzyme which catalyzes the formation of deoxyribonucleotides that this will lead to a rational approach for the design of specific inhibitors of this key metabolic site. These inhibitors should be useful in the chemotherapy of neoplasms. The ribonucleotide reductase from Ehrlich tumor cells has been separated into two non-identical components, neither of which has enzyme activity. However, the enzyme activity is reconstituted when both components are mixed. This project will involve the purification of each of these components to homogeneity. The study of the physical properties of the isolated components and the enzymatic activity of the mixture of components will be carried out. Studies will be carried out to relate the data obtained with the purified enzyme with the control of reductase activity in intact tumor cells.